Structure of MBE Grown InAs Quantum Dots studied by X-ray techniques

The heteroepitaxy of materials with a large lattice mismatch to the substrate is of special interest. E.g. small InAs islands on GaAs, are formed in the so-called Stranski-Krastanow growth mode if a critical thickness of a wetting layer is exceeded [1]. Our InAs quantum dot (QD) samples have been prepared by molecular beam epitaxy (MBE) in a UHV system with a base pressure of 1×10-11 mbar. Two types of samples were grown at substrate temperature of 450°C and 500°C, respectively. The amount of InAs deposited corresponds to a coverage of 2.1 ML (for 500°C) and 2.3 ML (for 450°C). In this report we present high resolution grazing incidence small angle X-ray scattering (GISAXS) and grazing incidence X-ray diffraction (GIXRD) experiments employing synchrotron radiation to study ordering, shape and strain status of uncapped InAs QD single layers experimentally. GISAXS [2]and GIXRD measurements were performed at the DESY undulator beamline BW1 with a wavelength of 1.17 Å. The incidence angle relative to the sample surface is 0.18°, which is below the total external reflection angle of 0.20°. The illuminated area on the sample is 16×2 mm2. Profiles of the scattered intensity are collected by a position sensitive detector (PSD), which is mounted parallel to the sample surface. The GISAXS measurements were performed along sample azimuthal orientations between –10 ° and 160° with steps of 5 ° for samples with 2.1 ML InAs coverage. Non-specular satellite peaks are observe